What indicates relief from power cut (4)
I believe the answer is:
phew
'what indicates relief' is the definition.
(expression of relief)
'power cut' is the wordplay.
'power' becomes 'p'.
'cut' becomes 'hew' (I've seen this before).
'p'+'hew'='PHEW'
'from' acts as a link.
(Other definitions for phew that I've seen before include "Gosh, I'm sweltering!" , "What a relief! It's hot!" , "I'm overheating?" , "thank goodness!" , "Recover unharmed" .)